1. Field of the Invention
The genus Diabrotica comprises many of the economically important field pests afflicting U.S. agriculture. In the adult stage the diabroticites, also known as cucumber beetles, inflict damage to a variety of fruits and fruit trees. They also feed on the leaves of cucumber and other vine crops including the squashes (Curcurbita) and melons (Cucumis and Citrullas). The larvae of several species are notorious for their damage to corn crops. The northern corn rootworm (NCR), D. longicornis barberi Smith and Lawrence, for instance, is an important corn pest in the upper Mississippi Valley region. The western corn rootworm (WCR), D. virgifera virgifera LeConte, and the Mexican corn rootworm (MCR), D. virgifera zeae Krysan and Smith, are significant pests in the midwestern and southcentral regions of the United States, respectively.
The continued search for alternatives to the widespread application of insecticides has led to the investigation of sex attractants as potential agents for use in integrated pest management. A number of economically important insects are currently monitored, partially controlled, or completely controlled by use of their own specific sex pheromone. The previous unavailability of Diabrotica pheromones has precluded application of this technology to the treatment of rootworms.
2. Description of the Prior Art
The production of a natural sex attractant by a species of Diabrotica was recognized by Cuthbert, Jr., et al. [J. Econ. Entomol. 57: 247-250 (1964)]. Female abdomen alcohol extracts (10 female equivalents) of the banded cucumber beetle, D. balteata LeConte, were reported to lure males of this species from distances as far as 49 ft. (15 m.).
In an unpublished Ph.D. thesis [University of Nebraska, Lincoln (1968)], Cates was able to show that for the WCR a mating or copulation stimulant was produced by 6-day-old virgin females, but he could not conclusively demonstrate the presence of a sex attractant. More recently, Ball et al. [J. Econ. Entomol. 66: 1051-1053 (1973)] reported that hexane extracts from field-collected WCR females were attractive to WCR males under field conditions, but relatively high concentrations of extract (i.e., 500-1,000 female equivalents) were needed for a significant response. These results suggest either the production of a pheromone of low potency, or else a misleading obseervation attributable to the presence of mated females in the field-collected sample. In a subsequent study by Guss [Environ. Entomol. 5: 219-223], it was reported that both WCR males and NCR males responded to an unfractionated hexane extract of filter paper on which WCR virgin females were temporarily held. The agent responsible for the behavior was not determined. Bartelt et al. [Environ. Entomol. 6(6): 853-861 (1977)] confirmed the mutual attractiveness of WCR and NCR males to WCR filter paper extract.